1. Field of the Invention
The present invention relates to resonators, and more particularly, resonators formed by collecting a plurality of spiral lines, for use in microwave or millimeter-wave band communications. In addition, the invention relates to filters, duplexers, and communication devices incorporating the resonator.
2. Description of the Related Art
As an example of a resonator for use in microwave bands and millimeter-wave bands, a hairpin resonator is described in Japanese Unexamined Patent Publication No. 62-193302. The size of the hairpin resonator can be reduced more than that of a straight-line resonator.
Additionally, another type of resonator capable of being made compact, a spiral resonator, is described in Japanese Unexamined Patent Publication No. 2-96402. In the spiral resonator, since a resonator line is formed of spiral shapes, a long resonant line can be arranged in a small area, with a resonant capacitor being provided as well, and a further reduction in the size of the resonator is achieved.
In the conventional resonator, since one resonator is formed by one half-wavelength line, an area where electrical energy concentrates and an area where magnetic energy concentrates are separately distributed on respective specified areas of a dielectric substrate. More specifically, the electrical energy is concentrated in proximity to the open-end portion of the half-wavelength line, and the magnetic energy is concentrated in proximity to the center thereof.
In such a resonator, an inevitable problem is a reduction in its characteristics due to an inherent edge effect of a micro-strip line. In other words, current concentrates in proximity to the external surface of the line. In this situation, since the current concentration occurs within a certain depth from the external surface of the line, even if the thickness of the line is increased, the problem of a power loss due to the edge effect cannot be solved.
Accordingly, in order to solve the problem described above, the present invention provides a resonator in which power losses due to the edge effect of a line are effectively suppressed. In addition, the invention provides a filter, a duplexer, and a communication device incorporating the resonator.
According to one aspect of the present invention, there is provided a resonator including a substrate and a set of lines comprising a plurality of spiral lines arranged thereon in such a manner that inner and outer ends of the spiral lines are distributed substantially along an inner periphery and an outer periphery of the set of lines respectively, the inner and outer peripheries being centered around a specified point on the substrate, and wherein the lines do not cross each other.
According to another aspect of the present invention, there is provided a resonator including a substrate and a set of lines comprising a plurality of spiral lines, each of the lines being in a position of rotational symmetry with respect to another spiral line. With this arrangement, when each line is seen in a cross-sectional view taken in the direction of the radius-vector (radius) of the set of lines, at the right and left sides of each spiral line, a line defining a point in each line through which current having substantially the same amplitude and phase flows through all of the lines is arranged at substantially a constant distance from a central point of the set of lines, with the result that an edge effect can be effectively suppressed.
According to another aspect of the present invention, there is provided a resonator including a substrate and a set of lines comprising a plurality of lines thereon, each line being indicated by a monotonically increasing or decreasing line in a polar-coordinate expression with one axis representing angles and the other axis representing radius vectors. Each line is arranged on the substrate in such a manner that the width of each line is within an angular width equal to or less than a value obtained by dividing 2xcfx80 radians by the number of lines n, and the width of the overall set of the lines is constantly within an angular width of 2xcfx80 radians or less at any arbitrary radius vector.
For instance, as shown in FIG. 2, when the position of the line is expressed in polar coordinates, in which the angle of the left end of a line at an arbitrary radius vector is xcex81 and the angle of the right end thereof at an arbitrary radius vector is xcex82, the angular width of the line is expressed by an equation xcex94xcex8=xcex82xe2x88x92xcex81. In this case, when the number of the lines is n, the angular width xcex94xcex8 of the line satisfies xcex94xcex8 2xcfx80/n. In addition, the angular width xcex8w of the overall set of the lines at an arbitrary radius vector rk is set to be 2xcfx80 radians or less.
With such a structure, a spiral line having the same shape as that of any given spiral line is disposed adjacent thereto. As a result, microscopically viewed, physical edges of the line are actually present, and a weak edge effect is generated at the edges of each line. However, the set of lines can be macroscopically viewed as a single line, so to speak. The right side of any given line is adjacent to the left side of another line having the same shape as that of the given line. As a result, the edges of the line in the line-width direction effectively disappear; in other words, the presence of the edge of the line becomes blurred.
Therefore, since current concentration at the edges of the line is very efficiently alleviated, overall power losses can be suppressed.
Furthermore, in one of the resonators described above, an electrode to which the inward end portions of the lines are connected may be disposed at the center of the set of lines. With this structure, the inward end portions of the lines, which are the inner peripheral ends thereof, are commonly connected by the electrode to be at the same potential. As a result, the boundary conditions of the inward end portions of the lines are forcibly equalized, so that the lines steadily resonate in a desired resonant mode, whereas a spurious mode is suppressed at the same time.
Furthermore, in the resonator of another aspect of the present invention, the equipotential portions of adjacent lines may be mutually connected by a conductor member. This arrangement permits the operation of the resonator to be stabilized without any influence on the resonant mode.
Furthermore, in the resonator of another aspect of the present invention, one end portion or both end portions of each of the plural lines may be grounded to a ground electrode.
In this situation, when only one end of each line is grounded, the resonator is a xc2xc-wavelength resonator. Accordingly, the desired resonant frequency can be obtained with only a short line-length so that the overall size of the resonator can be reduced. In addition, when both end portions of each line are grounded, electric field components at the grounded parts are zero, with the result that a good shielding characteristic can be obtained.
Furthermore, in the resonator according to another aspect of the present invention, each of the plurality of lines may be formed of folded lines. With this arrangement, the lines can be formed by using a simple structure that is obtainable by using film forming and micro-processing methods.
Furthermore, in the resonator according to another aspect of the present invention, the widths of the-plurality of lines and the distance between adjacent lines may be substantially equal from one end portion of the lines to the other end portion thereof. With this structure, the size of the resonator can be minimized.
Furthermore, in the resonator according to another aspect of the present invention, the width of each of the plurality of lines may be substantially equal to or narrower than the skin depth of the conductor material of the line. With -this structure, magnetic fluxes penetrate into each conductor line from both sides of the line and interfere with each other. Such interference realizes an even phase of the current density in the line. This means that the amount of ineffective current having a phase out of resonant phase can be reduced.
Furthermore, in the resonator according to another aspect of the present invention, each of the plurality of lines may be a thin-film multi-layer electrode formed by laminating a thin-film dielectric layer and a thin-film conductor layer. With this structure, the skin effect from the substrate interface in the film-thickness direction can be alleviated, which leads to further reduction in the conductor losses.
Furthermore, in the resonator according to another aspect of the present invention, a dielectric material may be filled in a space between adjacent lines of the plurality of lines. This can prevents short circuits between the lines, and when the lines are the above-described thin-film multi-layer electrodes, short circuits between the layers can be effectively prevented.
Furthermore, in the resonator according to another aspect of the present invention, at least one of the plurality of lines may be formed of a superconducting material. Since the resonator of the present invention has a structure in which a large current concentration due to the edge effect basically does not occur, the reduced loss-characteristics of a superconducting material can be fully used so as to operate the resonator with a high Q, at a level equal to or lower than a critical current density.
Furthermore, in the resonator according to another aspect of the present invention, the plurality of lines may be disposed on both surfaces of the substrate, and the periphery of the substrate may be shielded by a conductive cavity. With this arrangement, the symmetric characteristics of a resonant-electromagnetic field can be satisfactorily maintained, by which lower loss-characteristics can be obtained.
According to another aspect of the present invention, there is provided a filter including one of the above-described resonators, including a signal input/output unit. This permits a compact filter having reduced insertion losses to be produced.
According to another aspect of the present invention, there is provided a duplexer including the above filter used as either a transmitting filter or a receiving filter, or as both of the filters. This provides a compact duplexer having low insertion losses.
According to another aspect of the present invention, there is provided a communication device including either the filter or the duplexer, which are described above. This arrangement permits the insertion losses in an RF transmission/reception unit to be reduced, with the result that communication qualities such as noise characteristics and transmission speed can be improved.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.